LeCroy DDA 7 Zi series, Руководство оператора

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Operator's Manual
WP700Zi-OM-E-RevA
362
Figure 5-20. Illustrated above are two raised root cosine filters with
different beta. The diagrams show that applying this filter twice results in
a raised cosine response.
Gaussian
Band 1: Pass Band — DC to half power bandwidth% times modulation frequency,
pass; 3 dB down at half power bandwidth.
The shape of a Gaussian filter’s frequency response is a Gaussian distribution
centered at DC. The signal becomes more attenuated with increasing frequency. It is
not possible to specify a transition region or a stop band for Gaussian filters.
However, the BT value, a fraction of the symbol frequency, determines the filter’s
width, where:
B = half power bandwidth
T = bit (or modulation period)
IIR Filters
Infinite Impulse Response (IIR) filters are digital filters that emulate analog filters. The four types offered by the
DFP2 option are as follows:
x
Butterworth
x
Chebyshev
x
Inverse Chebyshev
x
Bessel
The Butterworth or "maximally flat" filter has the flattest amplitude response of all the available filters. The Bessel
filter is noted for its uniform phase response as a function of frequency. The following figure shows a comparison
between Butterworth and Bessel filters. Note that the Bessel filter has a wider transition bandwidth, but is linear
phase within the passband.